Abstract:

Accurately determining hydraulic fracture parameters is crucial for guiding the design of fracturing treatments and predicting single-well production. Currently, existing production-data-based fracture parameter inversion methods struggle to obtain fracture parameters for individual fracturing stages. To address this, leveraging the ensemble Kalman filter (EnKF) algorithm, an automatic inversion method for fracture parameters of each stage in tight gas reservoirs based on gas production profile testing was developed. To balance simulation accuracy and inversion efficiency, a reservoir production numerical simulation model based on embedded discrete fractures was established using the MATLAB reservoir simulation toolbox (MRST). Subsequently, the production of each fracture stage was simulated, and the EnKF was employed to iteratively update the fracture half-length and permeability for each stage, achieving automatic inversion of fracture parameters in tight gas reservoirs based on the gas production profile. Finally, the reliability of this method was validated through a designed case study, and it was applied to invert the fracture half-length and permeability of a field horizontal well. The research results indicated that: (1) when fracture orientation and spacing were fixed, increasing both fracture length and permeability enhanced tight gas production, but their impact on fracture production varied over time. Fracture permeability significantly influenced gas production in the first three months, while fracture half-length had a greater effect on production during the middle and late stages. (2) EnKF, as a sequential data assimilation method, captured the influence of fracture half-length and permeability on production at different stages. In the designed production profile fitting case, the relative errors of inverted fracture half-length and permeability were below 6.30% and 0.88%, respectively. (3) Based on the gas production profile of an actual horizontal well in a tight gas reservoir, EnKF could simultaneously invert the fracture half-length and permeability for each stage, with the relative error of the inverted fracture half-length below 8% compared to microseismic monitoring results. This method provides valuable guidance and reference for diagnosing hydraulic fractures in tight gas reservoirs.

Key words: tight gas, embedded discrete fracture, EnKF, gas production profile, fracture parameter inversion